A Nipple (or mammary papilla) is a small projection of skin containing the outlets for 15-20 lactiferous ducts arranged cylindrically around the tip. The skin of the nipple is rich in a supply of special nerves that are sensitive to certain stimuli.
The physiological purpose of female nipples is to deliver milk to the infant, produced in the female mammary glands during lactation.
In the male, nipples are often not considered functional with regard to breastfeeding, although male lactation is possible. Mammalian infants have a rooting instinct for seeking the nipple and a sucking instinct for extracting milk.